Fuel cells have been proposed as a clean, efficient and environmentally friendly source of power which can be utilized for various applications. A fuel cell is an electrochemical device that produces an electromotive force by bringing the fuel (typically hydrogen) and an oxidant (typically air) into contact with two suitable electrodes and an electrolyte. A fuel, such as hydrogen gas, for example, is introduced at a first electrode, i.e. anode where it reacts electrochemically in the presence of the electrolyte to produce electrons and cations. The electrons are conducted from the anode to a second electrode, i.e. cathode through an electrical circuit connected between the electrodes. Cations pass through the electrolyte to the cathode. Simultaneously, an oxidant, such as oxygen gas or air is introduced to the cathode where the oxidant reacts electrochemically in presence of the electrolyte and catalyst, producing anions and consuming the electrons circulated through the electrical circuit; the cations are consumed at the second electrode. The anions formed at the second electrode or cathode react with the cations to form a reaction product. The anode may alternatively be referred to as a fuel or oxidizing electrode, and the cathode may alternatively be referred to as an oxidant or reducing electrode. The half-cell reactions at the two electrodes are, respectively, as follows:H2—2H++2e−½O2+2H++2e−_H2O
The external electrical circuit withdraws electrical current and thus receives electrical power from the fuel cell. The overall fuel cell reaction produces electrical energy as shown by the sum of the separate half-cell reactions written above. Water and heat are typical by-products of the reaction. Accordingly, the use of fuel cells in power generation offers potential environmental benefits compared with power generation from combustion of fossil fuels or by nuclear activity. Some examples of applications are distributed residential power generation and automotive power systems to reduce emission levels.
In practice, fuel cells are not operated as single units. Rather fuel cells are connected in series, stacked one on top of the other, or placed side-by-side, to form what is usually referred to as a fuel cell stack. The fuel, oxidant and coolant are supplied through respective delivery subsystems to the fuel cell stack. Also within the stack are current collectors, cell-to-cell seals and insulation, with required piping and instrumentation provided externally to the fuel cell stack.
In conventional fuel cell systems, extensive piping and plumbing work is required since in operation fuel cell systems rely on peripheral preconditioning devices for optimum or even proper operation. For example, in the situation where the fuel gas of the fuel cell stack is not pure hydrogen, but rather hydrogen containing material, e.g. natural gas a reformer is usually required in the fuel delivery subsystem for reforming the hydrogen containing material to provide pure hydrogen to the fuel cell stack. Moreover, in the situation where the electrolyte of the fuel cell is a proton exchange membrane, since the membrane requires a wet surface to facilitate the conduction of protons from the anode to the cathode, and otherwise to maintain the membranes electrically conductive, a humidifier is usually required to humidify the fuel or oxidant gas before it comes into the fuel cell stack. In addition, most conventional fuel cell systems utilize several heat exchangers in gas and coolant delivery subsystems to dissipate the heat generated in the fuel cell reaction, provide coolant to the fuel cell stack, and heat or cool the process gases. In some applications, the process gases or coolant may need to be pressurized before entering the fuel cell stack, and therefore, compressors and pumps may be added to the delivery subsystems.
These peripheral devices require extensive piping and associated hardware, all of which leads to poor system efficiency. This results from significant energy losses occurring in lines or conduits as more power must be made available for supplementary devices such as pumps, fans, saturators etc, and hence the parasitic load is increased. In addition, hoses, pipes, valves, switches and other fittings increase the overall weight and size of the fuel cell system and complicate the commercial application thereof. This complexity poses problems in many applications, such as vehicular applications, where it is desirable that the piping and weight of the fuel cell system be minimized since strict size constraints exist. Furthermore, in vehicular applications, it is desirable for the fuel cell system to have good transient thermo-fluid response characteristics. This requirement makes it even more difficult to apply conventional fuel cell systems to vehicular applications, where relatively long pathways through hoses, valves, etc., can prevent rapid transient response characteristics being obtained.
Various efforts have been made to simplify the piping of fuel cell systems and hence reduce the size and weight thereof. However, to the applicants' knowledge, there has yet to be disclosed any fuel cell system that solves this fundamental problem.